In known methods and grinding machines for grinding grooves on workpieces, wherein in particular helically grooved or threaded workpieces are produced, the grinding wheel is profiled so that during grinding of groove into the workpiece, the outer positive form of profiling of the grinding wheel is generated as a negative formed groove in the workpiece. Even by using high performance and relatively durable CBN or diamond grinding wheels, the wear on the profile of the grinding wheel causes a deterioration of grinding result and correspondingly to a deviation from the nominal shape of groove in the workpiece, wherein during the grinding process also precision of profiling of the grinding wheel and sharpness decrease. Therefore, the profiling of the grinding wheel has to be newly profiled after a determined usage, i.e. it has to be dressed.
As a very efficient dressing method for profiling of above said grinding wheels, crushing has gained widespread acceptance. Crushing, which is frequently also called roll-in profiling, is a particular, accepted and appreciated method for rotational dressing for reproduction-precise profiling of metal or ceramic bonded diamond or CBN grinding wheels. Crushing is particularly used when precisely profiled tools have to be provided in large quantities.
Known crushing devices usually have crushing rollers, which are either driven and drive the grinding wheel by friction, when both are engaged to each other, or not driven, wherein the grinding wheel is driven, so that, when both are engaged to each other, the grinding wheel drives the crushing rollers by friction, i.e. by rotating the same. Due to a recent trend towards ever larger and more powerful grinding machines with powerful grinding spindle drives, driving of crushing rollers by means of driven grinding wheel has found increasing acceptance, i.e. the crushing roller is moving smoothly therewith, when the grinding wheel is engaged with the crushing roller. In order to achieve a high profiling precision on the grinding wheel, the crushing parameters have to be selected and applied with great care. Indeed, when crushing roller and grinding wheel are engaged to each other, either whole grains from the profiling coating of the grinding wheel or at least larger debris thereof are crushed or even ripped out. During crushing, care has also to be taken that the ripped grains are removed as fast as possible from the contact area between the crushing roller and the grinding wheel. The crushing process takes place at relative high pressures in the engagement area of crushing roller and grinding wheel, so that by possible deformations of the grinding wheel the profile to be formed is distorted during or after dressing. The parameters of the crushing roller and grinding wheel in a stricter sense or of the crushing roller spindle and grinding wheel spindle in a more general sense have therefore to be selected and applied so that said deformations are avoided or completely eliminated. If certain parameters, such as for example the relative advancement between grinding wheel and crushing roller, or the crushing pressure formed in the engagement area, is too large, a so-called rattling may occur, which has to be always avoided during the crushing process.
In DE 30 50 373 C2, a truing device for a numerically controlled profiling and planing machine is described. In this known truing device, a crushing device is positioned on the profiling or planing machine, which has its own drive. The truing of a plurality of profiled grinding wheels is provided, which are positioned one beside the other along their rotation axis, so that each profiled grinding wheel is associated to a truing roller. During the crushing, the truing roller is rolled under pressure over the grinding wheel, so that the grinding grains are crushed and broken free, wherein the peripheral speed of the grinding wheel and of the crushing roller are equal. Due to the truing roller for crushing directly positioned on the known grinding machine, the truing may be already integrated in the whole grinding process.
In DE 1 284 867 A, a universal grinding machine with a turret head is described, on which in its grinding spindle stock a so-called roll-in device is provided, with which the profile required for forming or plunge-cut grinding is rolled over the periphery of a grinding machine. The performing of the roll-in process in the sense of a profiling by crushing is not described. The profiling of the grinding wheel by this known roll-in device is performed, in fact, on the same grinding machine, although it is additionally performed between grinding operations or turning, drilling, rubbing and threading operations also performed on the universal grinding machine, in one single step.
In U.S. Pat. No. 4,555,873, a method and a device for grinding of workpieces by means of a profiled grinding wheel are described. On the grinding machine a truing device is also provided, with which form and sharpness of the grinding wheel may be restored. To this end, the grinding wheel's form and sharpness are restored by truing rollers, whose forms correspond to profiling of the grinding wheel between proper grinding operations. In this document, it is also described that the truing may be also performed during an interruption of the grinding process or even during the grinding, in a continuous manner. This document does not provide direct indications about a crushing, although it describes that the truing has to be considered as a process, which may be continuous or discontinuous. Methodological separations of the truing process are not described.
DE 41 04 266 A1 also describes a truing machine for profiling of a grinding wheel with a truing wheel. The described truing of the grinding wheel, i.e. the generation of the profiling of the grinding wheel required for precision of the grinding result is performed by truing wheels, which are rounded on their front sides, which wheels are spatially tilted around the front side of the grinding wheel during truing, in such a way that the required profile is achieved on the grinding wheel. The truing wheel is oscillating during the truing process about a respective tilting axis which is arranged at a distance from its respective peripheral front side and is transversal to the rotational axis. The truing wheel is essentially moved onto the grinding wheel. In this known truing machine the wear of the truing wheel has to be controlled.
JP 05138532 A provides a truing device for CBN grinding wheels, which dress the grinding wheel so that it may be used both for pre-grinding and finishing. The truing wheel has so called crushing grains and single abrasive grains, which are mixed in the truing coating. The truing is performed in one step and comprises the truing from axial front sides of a cup-shaped grinding wheel.
U.S. Pat. No. 3,435,814 already describes a crushing device for crushing of profiled grinding wheels, which are fixed on a grinding machine. The crushing device has the form of a crushing roller and is placed on the grinding wheel for truing the same. A drive for the crushing roller has to ensure that the peripheral speed of the crushing roller and of the grinding wheel are identical. When the crushing roller and the grinding wheel are engaged to each other, only the grinding wheel drives the crushing roller. The crushing process is performed in one step, and the crushing roller is subsequently separated from the grinding wheel.
The company brochure of Saint Gobain Abrasives also describes how a roll-in device for truing of a profiled grinding wheel should be part of the machine and be fixedly mounted on the same. A time-consuming tool replacement may therefore be avoided. The grinding wheel has to be preferably driven and the profiled roller should be smoothly driven by the same during truing. For first profiling as well as for subsequent profiling processes, specific profile rollers are required. In this known device, it is required that after the pre-profiling, the profiling rollers are replaced. This is disadvantageous in that positioning errors and profiling errors may occur on the grinding wheel.
All of the already-described truing or crushing methods and devices have in common that the crushing may neither be performed for a specific grinding task nor the parameters ensuring a high flexibility of the crushing process itself may be taken into account.